Harnessing the MYB51/SWEET20 module to increase soybean yield by facilitating sugar supply to sink organs.

Key message: GmMYB51-GmSWEET20 plays an important role in soybean yield formation by promoting carbohydrates distribution and reducing flower and pod abscission. These insights provide a new molecular framework for soybean yield improvement. Enhancing the supply of carbohydrates into sink tissues is a promising strategy for improving soybean (Glycine max) yield. However, the underlying molecular mechanisms remain poorly understood in soybean. In this study, transcriptome comparison analysis of Zhongdou 29 (ZD29, a low-yielding variety) and Zhongdou 32 (ZD32, a high-yielding variety) identified a SWEET (Sugars Will Eventually be Exported Transporter) gene, GmSWEET20, which exhibited higher expression level in the petioles and stems of ZD32 and functioned as a sucrose and glucose transporter. Overexpression of GmSWEET20 resulted in increased pod number and higher yield by facilitating carbohydrate accumulation in sink tissues and reducing flower and pod abscission. While knock-down of GmSWEET20 and its three homologous genes with RNAi technology decreased pod number and yield. GmMYB51, which also exhibited higher expression level in ZD32 than in ZD29, could bind to the promoter of GmSWEET20 and activate its expression. We further confirmed overexpression of GmMYB51 also enhance efficient supply of carbohydrates to sink organs and increase pod number and yield through upregulation of GmSWEET20 expression. Taken together, our findings identified a novel regulatory module composed of GmMYB51 and GmSWEET20, which enhances carbohydrate supply in sink tissues, thereby leading to improved pod number and yield. These insights provide a molecular framework for yield improvement strategies of soybean.